Trifluridine (also called: α,α,α-trifluorothymidine. Hereinafter, also referred to as “FTD”) exerts an antitumor effect due to an action for inhibiting thymidylate formation and an action for inhibiting DNA synthesis by incorporation into DNA. On the other hand, tipiracil hydrochloride (chemical name: 5-chloro-6-[(2-iminopyrrolidin-1-yl)methyl]-pyrimidine-2,4(1H,3H)-dione hydrochloride. Hereinafter, also referred to as “TPI”) has an action for inhibiting thymidine phosphorylase. It is known that the antitumor effect of FTD is enhanced by the TPI suppressing the degradation of FTD in vivo caused by thymidine phosphorylase (Patent Literature 1). Currently, an antitumor agent containing FTD and TPI in a molar ratio of 1:0.5 (hereinafter referred to as “FTD/TPI combination drug”) is under development as a therapeutic agent for solid cancers, for example, colorectal cancer (Non Patent Literatures 1 and 2).
Further, irinotecan hydrochloride hydrate (hereinafter, also referred to as “CPT-11”) is a camptothecin derivative whose active metabolite is SN-38 and which suppresses the synthesis and transcription of DNA by inhibiting topoisomerase I, thereby to exert an antitumor effect. CPT-11 is clinically used as a therapeutic agent for a wide range of cancer types including, for example, small cell lung cancer, non-small cell lung cancer, cervical cancer, ovarian cancer, gastric cancer, colorectal cancer, breast cancer, squamous cell carcinoma, and malignant lymphoma (Non Patent Literature 3).
Further, when FTD and SN-38 were allowed to act on a colorectal cancer cell line, a synergistic cytotoxicity was observed and thus a combination therapy using an FTD/TPI combination drug and CPT-11 has been expected (Non Patent Literature 4).